[flash]

the stability you feel is also speed scrubbing - this was somthing i had to learn the long hard way - i kept getting beat by the same car and wondered why - then i drove the car that was beating me, and though i felt like it was less stable, it was actually faster - then i did the same spec on my front end and bingo! a full second off my lap times



this is where complicated geometry gets involved - roll center and camber change drawings showed me what was going on - turned out that stable was not necessarily fast

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[Eric_K]

Yeah, but if what you learned was in an MGB (if that is what you are talking about) then the suspension is of a completely different design. Castor settings on a MacPherson strut will be completely different. I doubt the castor settings will have that much effect on lap times in a 968.



Eric

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[flash]

it was an mgb - was very different for sure - it was unequal length upper and lower control arms - that's why i was saying that geometry was involved here - i haven't lain out the drawings yet to see what happens on this supension - still playing with that one - just set it up today with some different specs - not sure if i like them yet or not

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[Eric_K]

What's an "1/8" in real money  do you know what that is in degees.

I checked my alignment sheet and I have .24 degrees total toe in (.12 per side). Whether that works out to 1/8" - I'm too lazy to check. BTW my castor max'd at 4.1.



Also, when I had a track/street car I used the same settings but with a degree less camber front and rear.



Eric

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[heyou]

[quote name='Eric_K' date='Apr 21 2005, 05:02 AM']I checked my alignment sheet and I have .24 degrees total toe in (.12 per side). Whether that works out to 1/8" - I'm too lazy to check. BTW my castor max'd at 4.1.



Also, when I had a track/street car I used the same settings but with a degree less camber front and rear.



Eric

[right][post="3575"]<{POST_SNAPBACK}>[/post][/right][/quote]



thanks for that, i'll go ahead and get these setting done. Does anyone feel that the car should be correctly loaded with at least half a tank of fuel and a driver in the car while doing the toe settings? I know that toe measurments change with movement of the susspension and therefore it make a difference when setting such a small amount of positive toe and then loading up the car with fuel and driver could easily change it from small positive toe a small toe out situation!!



cheers



Del

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[flash]

YES!!!! YES!!!! YES!!!! YES!!!! YES!!!!

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[heyou]

[quote name='flash' date='Apr 21 2005, 03:38 PM']YES!!!!  YES!!!!  YES!!!!  YES!!!!  YES!!!!

[right][post="3587"]<{POST_SNAPBACK}>[/post][/right][/quote]



LOL, do i take it you agree with me about pre-loading the car whilst the toe settings are being performed?



Del.

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[Eric_K]

If you are going to the trouble of having the correct weight in the car etc. (and you have height adjustable coilovers) you should get the car corner balanced as well.



I finally looked at the pictures of your tires. They don't look thaaat bad for having 660 track miles on them. Reducing your toe and having a decent amount of camber should help with the outside wear some, but track tires just don't have long lives anyways. Ask my wallet. <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



I currently have a set of Toyo RA-1's that have nearly 1000 racing miles and they still look good. They may not be the fastest, but what a great tire. I just can't kill them - no matter what I do.



Eric

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[flash]

finally somebody is getting it - you wouldn't believe how many "conversations" i've had about some shop's failure to load the car properly when doing an alignment - failure to do so changes things dramatically, and small changes on these cars make huge handling and tire wear differences - if you take a look at the alignment specs thread in the technical section, you will see that the differences in specs are very small, but the handling changes are very dramatic



so, yes, load the car as you normally would, have a half tank or so of gas, and you or an equivelant amount of weight in the driver seat - this gives you the best nominal condition

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[mikew968]

I just redid the suspension on my 968. I added the Leda single adjustables with 450# fr and 500# rear springs. I also have racers edge camber plates. I am running -3.0 camber F and -2.5 rear. I am running about 1mm toe-out on the front with either 0 or 1mm toe-in rear.



The shocks were set mid way for Mid-Ohio and te car was very neutral and drove very well. Turn-in was much better than with stock.



Mike

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[moses]

I'd like to ask a question about camber plates in almost total ignorance, suspensions are pretty much black boxes to me.



Because I've been taking long road trips too often on the interstates I would like to increase my (purely street) car's tendency to return to center, or straight-line stability, call it what you want. I understand that the simplest way is to increase the caster, but i also understand that the caster isn't adjustable on a stock 968. Are those two beliefs right?



If so, i would like to repeat the earlier question and ask if anybody knows of a particular camber plate that doesn't sacrifice ride quality or noise but would give me the caster adjustment. Or if there is a smarter way to add a little more stability. I'm willing to sacrifice steering effort but I love the way these cars handle on "real" roads (roads with turns and instead of traffic have those funky yellow signs with squiggly lines up the middle) and don't want to turn it into another car, just make a long boring drive a little less effort.



Living in central PA is great for back roads but the local joke is that civilization is 4 hours in every direction.

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[flash]

front castor is adjustable - rear is not



castor will help with high speed stability and return to zero, but it is not the only thing that does this



any solid bearing type camber plate will increase a certain amount of harshness on bumps - this will also tend to translate as noise - whether or not it is tolerable, like any noise in a car, is highly subjective



what tires are you running, and what pressures? this can have a lot to do with it



also, front toe setting is important when talking about straight line stability - do you know what your toe setting is?

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[moses]

Took me a while to find the printout from my last alignment:



Camber: 0.0 deg (both wheels)

Caster: left 2.5 deg right 2.8 deg

Toe-in: 1/32 inch (both wheels, can't help the units, that what the paper says)

Tires: P Zero Nero M&S stock size (205 & 225) on 16 inch rims @35 psi all around



After I learned here the caster is adjustable i looked at the shop manual, duh, and sure enough.



I'll talk to my alignment shop, they're obviously not up to speed on this car and since the caster is right at the lower limit it should be adjustable up some. And it explains my car's reduced tracking. Obviously I don't need to replace hardware before i do a simple adjustment.



thanks for the help.

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[flash]

this is a far too common problem, and is very frustrating to hear - you, the consumer, expect you are getting what you are paying for, and in the end you aren't



take it to a different shop - the machine they are using is an old one - newer machines all measure in hundredths of a degree and not inches - also make sure it has been recently calibrated - they go out of whack easily



get a full 4 wheel alignment and make absolutely sure you have your ride height set correctly with the car properly loaded (your weight in the driver seat, normal stuff in the car, and about a half tank of gas) - this job will require some special tools (eccentric adjuster and some thin wrenches)- if they don't have them, they are the wrong shop



get a before and after printout - your current toe is the wrong way, castor is low, and camber is low (should be in the negatives) - that's just the front - any idea what the rear is? that will also seriously affect tracking

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[heyou]

I'm getting the impression from reading about caster that, and especially with MacPherson struts, that more positive caster is a good thing!



It increases the negative camber, when cornering, as the wheel leans over into the corner (good for the track), it increases straight line tracking/stability, it can make for harder work to turn the steering wheel (but not a prob. with power steering).



Del.

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[flash]

i may end up agreeing with you - i just reduced my front castor, and the car feels light and loose - i may have gone too far - i made a bunch of other changes too, so i have to sort through it all first, but it may end up being exactly that

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